If the computer starts, you can solveproblems, without resorting to disassembly of the system unit. While the computer is starting, carefully watch the bottom of the screen: there should appear information with the necessary commands and ways to perform them (1-2 lines). In order to reset the BIOS, you must first find on this panel a key, when you click on it, the BIOS window opens. Sometimes this is a Del key, but it may be different, it all depends on the version.
If you change the BIOS settings, the computer does notrun at all, you have to reset the settings manually. First, carefully remove the cover from the computer. Then find the documentation for the motherboard - without it it will be difficult, especially if you do not have experience in such actions. Find the image of the board in the manual and look at the location of the key elements on them. Your goal is a BIOS battery. After you find it on the picture, proceed to the search on the board. For instructions on how to remove the battery, see the documentation. The battery should be removed for 20-30 seconds, then returned to the place.
If and after this procedure there are problems(the time is reset, some programs constantly "forget" the settings), that is, it makes sense to replace the battery, because it most likely has exhausted its resource (2-3 years). Replacing the battery, you will spare yourself questions about how to reset the bios, because it will automatically reset to the factory settings.
Remember that when setting up a computer,using BIOS, you take full responsibility for yourself. This method requires certain knowledge, and change something only on the advice of friends is not necessary - can go sideways. Sometimes after unsuccessful experiments with "optimization" the user does not have any other way out, except how to reset the BIOS. For example, a user can accidentally remove the thermal protection of the processor and that at the first significant overheating will just burn out - there's a need to reset the settings one by one. In other words, be careful and do not set up what you do not have the faintest idea about.